FWIW, in the case of Solar City he consistently emphasizes in his interviews that he has to basically "just show up at board meetings and hear the good news" and that most of the credit goes to the guys in charge there. But anyway, I'm deeply impressed by this guy, especially since he is not only CEO but also Chief Designer at SpaceX and Product Architect at Tesla.

I was mainly referencing Solar City which he doesn't really run.

A good example of someone who doesn't focus on one thing and is hugely successful is Richard Branson. Virgin Group has more than 400 companies.

Incorrect. Steve was CEO of Pixar and Apple at the same time. He found it to be exhausting. In Isaacson's book Steve believe this weaken his immune system which led to his cancer, which Isaacson discredited.